In the past, there has been extensive description in the patent and other technical literature of photoelectrophoretic imaging processes. Descriptions of photoelectrophoretic imaging processes are contained in U.S. Pat. Nos. 2,758,939 by Sugarman issued Aug. 14, 1956; 2,940,847, 3,100,426, 3,140,175 and 3,143,508, all by Kaprelian; 3,384,565, 3,384,488 and 3,615,558, all by Tulagin et al; 3,384,566 by Clark; 3,383,993 by Yen; and U.S. Pat. No. 3,976,485 by Groner.
In each of the foregoing photoelectrophoretic imaging processes an imaging layer comprising electrically photosensitive material is subjected to the influence of an electric field and exposed to an image pattern of electromagnetic radiation to which the electrically photosensitive material is sensitive. The electrically photosensitive material is caused to migrate imagewise in the layer to form a record of the imaging electromagnetic radiation.
Regardless of the particular photoelectrophoretic imaging process employed, it is apparent that an essential component of any such process is the electrically photosensitive material. To obtain an easy-to-read visible image it is desirable that the electrically photosensitive material be colored.
Generally useful electrically photosensitive compounds for photoelectrophoretic imaging have been selected from known classes of photoconductive compounds which have been employed in conventional photoconductive elements, e.g., photoconductive plates, drums, or webs used in electrophotographic copier devices.
For example, both Sugarman and Kaprelian in the abovereferenced patents state that electrically photosensitive materials useful in photoelectrophoretic imaging processes may be selected from known classes of photoconductive materials. Also, the phthalocyanine pigments described as useful electrically photosensitive material for photoelectrophoretic imaging processes in U.S. Pat. No. 3,615,558 by Tulagin et al have long been known to exhibit useful photoconductive properties.
However, many of the photoconductive materials chosen for use in photoelectrophoretic imaging processes have been inadequate in various aspects such as low electrical photosensitivity and poor color. Accordingly, there exists a continuing effort to find materials which possess both useful levels of electrical photosensitivity and which exhibit good colorant properties.